Hot melt adhesive systems have many applications in manufacturing and packaging. For example, thermoplastic hot melt adhesives are used for carton sealing, case sealing, tray forming, pallet stabilization, nonwoven applications including diaper manufacturing, and many other applications. Hot melt adhesives often come in the form of pellets or particulates, which are generally referred to as pieces, and are contained in or provided from an adhesive supply, such as a tank or hopper. The hot melt adhesive pieces can be heated and melted by a melter, and liquefied hot melt adhesive can be pumped to a dispenser, such as a dispensing gun or other applicator which applies the hot melt adhesive to a substrate. Hot melt adhesive, in its pre-melted state (referred to herein as hot melt adhesive pieces, or unmelted hot melt adhesive pieces), can be provided in a variety of shapes and sizes, ranging from small bb-sized pieces, to larger sized pieces which are sometimes referred to as “chips” and still larger “pillows” that are several inches in dimension. Hot melt adhesive pieces may be moved from the adhesive supply to the melter as part of an automated filling operation.
For example, air-driven, or pneumatic, transfer systems use the force of flowing air to move hot melt adhesive pieces from an adhesive supply to a melter. In a known arrangement, a transfer conduit connects the adhesive supply with the melter, and an air pump is operated to generate an air flow that moves hot melt adhesive pieces through the transfer hose from the adhesive supply to the melter.
Environmental conditions, however, can interfere with the movement of hot melt adhesive pieces from the adhesive supply to the melter. In particular, temperature and/or the amount of time that the hot melt adhesive pieces have been in the adhesive supply may affect the movement of the hot melt adhesive pieces. For example, as the environmental temperature increases, the hot melt adhesive pieces can begin to soften and stick together to form clumps of hot melt adhesive.
Pneumatic transfer systems have a limit relative to the size and weight of the hot melt adhesive that they can transfer in a cost effective manner. Large clumps of hot melt adhesive can be too large to fit through a transfer hose and travel between the adhesive supply and the melter. Large clumps can also be too heavy to be moved by a given pneumatic transfer system. If a melter is not provided with an appropriate flow of hot melt adhesive pieces, the melter will not be able to provide liquid hot melt adhesive to a dispenser. This would cause an undesirable disruption of a dispensing operation.
In addition, as hot melt adhesive pieces begin to stick together in the adhesive supply, features can be formed in the adhesive supply that also tend to deprive an adhesive melter with an appropriate flow of hot melt adhesive pieces. For example, hot melt adhesive pieces that have stuck together can create a clump or an even larger formation in the adhesive supply. Such a formation will not be moved out of the adhesive supply by the pneumatic transfer system. In addition, the formation is likely to block the flow of hot melt adhesive pieces from the adhesive supply to the transfer conduit that connects the adhesive supply with the melter. Moreover, clumps or large formations of hot melt adhesive tend to cause nearby hot melt adhesive pieces to stick to them, and this process can lead to substantially large formations in the adhesive supply.
In addition to increased temperatures, the amount of time that hot melt adhesive pieces have been sitting still in an adhesive supply can also cause problems for moving the hot melt adhesive pieces to a melter. The longer hot melt adhesive pieces sit in the adhesive supply, they can begin to stick together, leading to similar problems as those discussed above.
Therefore, there is a need for an improved hot melt adhesive supply system that overcomes the shortcomings addressed above.